Percussion instruments have been in widespread use around the world since long before recorded musical history. They are instruments which are struck, or shaken or scraped, in order to produce a sound, and come in numerous different varieties. Many percussion instruments that are in common use today require the player to exert a great deal of energy while playing the instrument, in order to produce the required level of sound. A proportion of this energy is translated directly into sound energy, which gives each instrument its dynamic range and characteristic prominence over other instruments such as strings. However, much of the energy input to a percussion instrument can nonetheless be wasted.
Percussion instruments (and indeed all musical instruments) can be classified according to the Hornbostel-Sachs system for musical instrument classification. This characterises percussion instruments into two broad categories: idiophones and membranophones.
Idiophones are those instruments which produce sound primarily through the actual body of the instrument vibrating. Examples of idiophones are the xylophone and marimba, which are tuned idiophones, or a plethora of shakers and rattles, which are known as shaken idiophones. Shaken idiophones include vessel rattles, or simply shakers, in which rattling objects enclosed in a hollow vessel strike against each other or the walls of the vessel or both. These instruments are usually held in the hand of the player and shaken rhythmically.
The motion required to produce a musical sound from a shaken idiophone needs to vigorously shake the rattle members within, and more often than not requires that the player oscillate the instrument rhythmically back and forth. Rattle members are often a small portion of the mass of the instrument as a whole, and so a large amount of kinetic energy goes into moving the body and not making sound.
Membranophone is a term which broadly covers all types of drum, that is, an instrument which has a body and a tightly stretched membrane or skin, usually over a hollow body which vibrates in a way dependent on the manner in which the instrument is played. Most membranophones are struck with either the hand or a beater, but some involve rubbing the skin (such as the bodhran) and others use air currents to vibrate the membrane (in the case of a kazoo). Many drums are designed to be played manually, that is, by hand without a stick or a beater. Examples include conga drums, bongos, tabla etc.
The djembe is a very popular hand drum, originating from West Africa. The drum can produce a variety of different sounds and tones, depending on the vibrational modes introduced into the skin, which depend on the force applied and location in which the drum is struck.
A drummer playing a drum with either his or her hands or with sticks or beaters will impart a great deal of kinetic energy into the drum skin, and also to the body of the drum. When playing a typical hand drum, for example, the player hits the drum skin with the fingers extending toward the middle of the drum, and the palm and heel of the hand transmits most of the playing force to the interface between the skin and the body or side walls of the drum. In some instances, a player may wish to make an entirely different sound altogether, and strike only the wall of the drum. When playing the snare drum, or modern drums, a rim shot is where the player strikes an O ring of metal that is used to tension the drum skin.
Many mounting technologies have been developed to minimise the vibration of the body of drums during their playing, while minimising changes to the acoustic properties of the drum or percussion instrument. Often a set of drums (congas, or rock drums, for example) will be mounted on secure metal frame mounts to keep them in position during playing.
Electronic musical instruments are known which convert movements made by the player into electrical signals which are sent to a processor and onward to output means to output sound—for example electronic percussion or keyboard instruments. In such instruments, only a signal representative of the input is generated. The signal is instantaneous and although a digital value indicative of its characteristics may be stored or processed, energy from the input is not stored or re-used. The creation of the electrical signals is not designed to maximise the amount of electrical energy based upon the amount of energy imparted by the player.
Microphones and other recording or “pick-up” devices, when placed in or near instruments have to be designed such that they do not detrimentally alter the acoustic properties of the instrument, and therefore the amount of energy extracted for their function must be minimised. The focus of such devices is on the fidelity of the output signal, while minimising the energy extracted from the instrument to avoid affecting the musical quality, timbre or tone.
Children's toys are also items which can be subjected to significant input of kinetic energy, either during normal use as they are played with, thrown, carried or shaken by children, or also where they are toy instruments.
The reclamation of energy is a well-known problem and an increasing concern with the population's increasing electrical energy needs. It is known in transport technology, such as in cycling, for example, to use the kinetic energy of a person created while riding a bicycle connected to a dynamo-electric circuit to charge a mobile phone, for example.